1. Field of the Invention
The present invention relates to a bus control system, and more particularly, to a bus control system applicable for bus trace for monitoring the operational status of a micro processor.
2. Description of the Prior Art
There is disclosed a multi-chip module evaluating device in, for example, Japanese Patent Laid-Open No. 5-120160 (1993), which traces wiring signals between a floating operation unit and a data memory. The wiring signals which are closed in the module, substrate of a multi-chip module are traced by connecting, via a prober, a leader pad on the module substrate with a monitor unit, which comprises a memory, an address generator, and a comparator. This evaluating device can directly trace a wiring signal, without using any test element group (TEG). Therefore, this evaluating device is employed for tracing wiring signals, because an evaluation merely by signals extracted to external pins is not sufficient, especially in the case of mounting LSI packages on the module substrate.
The above-mentioned conventional device has the following disadvantages:
Firstly, leader pads are necessary for tracing the wiring signal, because the wiring signal is closed in the module substrate. Accordingly, the above-mentioned evaluating device is not of any use for a multi-chip module which is small-size-oriented, because the number of pads increases with an increase in the number of wirings which completes in the module substrate, which in turn results in an increase in the pads area.
Secondly, a testing device is exclusively necessary for bus trace. Specially designed probers are required for connecting themselves with the special leader pads on the module substrate.
Thirdly, the reliability of bus trace is lowered. When the leader pads are inferior due to a manufacturing process, then the module substrate can not be traced completely.
An object of the present invention is to provide a bus control system with improved reliability for easily tracing signals on the bus of a micro processor via a bus interface, when evaluating bus interface peripheral circuits and software for a micro processor board. Another object of the present invention is to improve the reliability of the evaluation system.
According to the present invention, there is provided a bus control system, which comprises a micro processor, a main memory and a system control register each of which is accessed via an internal bus by the micro processor, and a bus interface.
The bus control system of the present invention further includes a tracing means for tracing every access, by the micro processor, to the main memory, to the system control register, and to the bus interface by using an external bus via the bus interface.
According to the present invention as explained above, the following effects are obtained:
Firstly, the leader pads become unnecessary for tracing the wiring signal which is closed in a module substrate, because every status of an internal bus can be traced via the bus interface.
Secondly, a high density mounting board such as a multi-chip module can be furthermore integrated in a higher density, keeping the compatibility of function of the internal bus tracing, because the exclusive pads become unnecessary and the wide mounting area is preserved.
Thirdly, bus trace becomes easy, because ordinarily available instruments can be used for bus trace at the external bus connected with bus interface, or the peripheral circuit of a micro processor board.